Jeff and Steven McDonald have rekindled their band's musical angst with a new album and a co-headlining spot at FYF Fest.

Redd Kross' Jeff McDonald has a simple rule when it comes to lyric writing: "If it doesn't give me a stomachache, I like it."

Turn that sentence into a math equation and one reaches the following conclusion: The co-founder of Redd Kross, a group that's long been a staple of L.A.'s underground rock scene, has composed at least 10 songs in 15 years that don't didn't induce nausea.

"Researching the Blues," released this month on North Carolina indie Merge Records, sees McDonald, 49, re-anchoring the band he formed with his younger brother, Steven, 45. The two have been playing together since they were budding middle-school punk rockers in suburban Hawthorne, offering a more adolescent and humorous take on the genre than their harder-edged mentors Black Flag.

In the early '80s, sources of frustration for the brothers McDonald included the jocks and surfers who inspired the song "I Hate My School," the racist kids (and parents) down the street, and the dreaded "pseudo-intellectuals."

FOR THE RECORD: Redd Kross: A caption in the Aug. 31 Calendar section under a photo of brothers Steven and Jeff McDonald of the band Redd Kross said they would be performing at this weekend's FTF Fest in downtown Los Angeles. The event is called the FYF Fest. —

But on a recent Sunday afternoon at Victor's restaurant in Hollywood, with the band set to co-headline this weekend's two-day FYF Fest downtown, it's clear that while Redd Kross might have an older point of view than Sleigh Bells, Yeasayer, Warpaint and other younger FYF acts, the droll brothers' attitude hasn't changed much.

Their new song "Uglier," for instance, takes a fed-up look at the outside world and then brings the focus closer to home in its final moments, where it deals with some of the less glamorous aspects of aging. "You're getting uglier," Jeff rasps matter-of-factly. "I'm getting uglier."

"I think it's really interesting now that the questioning of an age limit in rock is less and less relevant," Steven says, reflecting on Redd Kross' evolution from cult favorites to rock elders. "With free music and more music available, people like what they like. It doesn't matter if it's an 18-year-old or a 45-year-old."

Redd Kross, which bounced from record label to record label as much as it ricocheted between impassioned guitar-rock and animated, hook-filled power-pop, has found a home at Merge Records. The indie, which also works with Arcade Fire and Spoon, is run by longtime Superchunk anchors Laura Ballance and Mac McCaughan, whose last album, 2010's "Majesty Shredding," was a statement of no-nonsense, rock 'n' roll perseverance.

"This record, like the Superchunk record, does reflect that there's validity to that older voice, whether or not it's that teenaged rock archetype," Steven says. "You can have middle-age angst, or a middle-aged love of teen angst. If you mean it, it's vital."

But what took so long? The band was persuaded to reunite after almost a decade apart for a 2006 Spanish festival. The lineup that came together was the same one from its 1987 album "Neuorotica." That album had begun to reach a new audience after it was reissued in 2002 by Go-Go's guitarist Charlotte Caffey and That Dog's Anna Waronker (Caffey is married to Jeff and Warnonker to Steven). Recording on a new album began in earnest in 2007.

Talk to the brothers and numerous reasons will be offered as to why the new songs sat in the vaults for a number of years. Gigs with other bands, production work, children and even Steven's 12-month employment as an A&R exec for Warner Bros. He helped bring rootsy pop-rockers Dale Earnhardt Jr. Jr. to the label and then ultimately lost interest in the corporate life.

"It was eye-opening, the one year I spent being a full-time staffer at a label," Steven says. "I was trying to get the best deals for everyone, but it was weird. Why was I trying to get a band's hard-earned live cash and merch money? I should be focusing on my own band — my own band's merch money and live money."

And yet it's not as if the Redd Kross vaults are overflowing with material. Reflecting on his brother's songwriting pace, Steven says, "I don't think Jeff can be accused of being corrupted by his ambition."

"Are you," Jeff interjects, "saying I'm not ambitious?"

Such back and forth fills much of an hourlong conversation. Jeff reveals that he has songs for another Redd Kross album and even an album title and genre for it.

"It's adult rock," he says, only to be admonished by his brother.

"That word has connotations," Steven says.

Fine, says Jeff, he'll use the term "in private."

Meanwhile, Merge is waiting — for now.

"We hope this will be more than a one-off," Merge's Ballance says. "But it has been 15 years since their last record, so if it takes them another 15 years, then who knows?"